Method for forming an information recording medium having information on spare area, and method and apparatus for recording/ reproducing data to/ from the medium

ABSTRACT

This invention provides an information recording medium, and a method and apparatus for writing to/reading from a recording medium in which a starting point of a spare area is variable relative to a starting point of a data area. Information concerning a variable boundary between the data area and the spare area is stored on the recording medium. A method and apparatus for writing/reproducing data to/from the recording medium is also provided. In a preferred embodiment, the recording medium is an optical disc.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus formanufacturing an optical recording medium in which ratios of spare areato data area differ from one zone to another, depending on each zone'slocation in the radial direction, and which has information needed todiscriminate data area and spare area in each zone, and to a method andapparatus for writing/reproducing data to/from the optical recordingmedium.

[0003] 2. Description of the Related Art

[0004] Optical discs have come into wide use since the advent of CD(compact disc). The demand for optical discs is expected to growsteadily with popularization of DVD (digital versatile disc). Opticaldiscs include read-only discs such as CD-ROM and DVD-ROM, write-oncediscs such as CD-R and DVD-R, and rewritable discs such as CD-RW andDVD-RAM. Standard formats of CD-RW and DVD-RAM have been released andstandardization for DVD-R is in progress.

[0005] As shown in FIG. 1, the rewritable physical area of DVD-RAM has alead-in area, a user area, and a lead-out area. The user area is dividedinto 24 contiguous groups, so-called zones, and guard areas are situatedbefore and behind each zone. Each zone is made up of a data area forrecording data and a spare area for replacing a defective portion of thedata area.

[0006] The data area is made up of a plurality of ECC (error correctioncode) blocks, each consisting of 16 sectors. The location of each sectoris specified by a physical sector number (PSN) that is given uniquely toeach sector. That is, a PSN is assigned to every sector from the innerdiameter to the outer diameter. While recording, LSNs (logical sectornumber) are assigned to only non-defective sectors sequentially.

[0007] Tracks located in the same zone have an equal number of sectors.As the track length is increased by the angular length per sector frominside out, the number of sectors per track is increased by 1 and a newzone identification number is assigned. For every zone, CLV (constantlinear velocity) is employed, but CAV (constant angular velocity) isused for tracks within the same zone.

[0008] For rewritable optical discs such as DVD-RAM, defects that arisein their recording surface should be managed to achieve highly reliablewrite/reproduction operation in a manner that data is not written tosectors in which read-out errors are detected beyond a predeterminedlevel (hereinafter referred to as “defective” or “bad” sectors). Toaccomplish this, defect management is performed such that addresses ofdefective sectors are stored in defect management tables on the opticaldisc and access to data on such defective sectors is prohibited. Asshown in FIG. 2, if a defective sector is detected during a writeoperation, it is replaced by the next valid sector (slippingreplacement). When a bad sector is detected during a reproductionoperation, an ECC block containing the bad sector is replaced by aunused ECC block in a spare area, as shown in FIG. 3 (linearreplacement).

[0009] Defect management information, or physical addresses of defectivesectors within the data area are stored in a DMA (defective managementarea), which is provided in four places, two in a lead-in area and theother two in a lead-out area, as shown in FIG. 1, to protect against thedefects which may arise in the four DMAs themselves.

[0010] The DMA is made up of two ECC blocks, or 32 sectors. The firstECC block consists of one sector for a DDS (disc definition structure)and 15 other sectors for a PDL (primary defect list). Sixteen sectors ofthe second ECC block are all used for a SDL (secondary defect list).

[0011] As shown in FIG. 4, each track of DVD-RAM is, physically, made upof a recording portion A for recording user data and a header portion Bfor providing positional information and indicating whether the track isa groove track or land track. Groove tracks and land tracks are arrangedalternately, and wobble boundaries C are formed between groove tracksand land tracks. The wobble shape of the boundary C is used to generatea periodic signal of low frequency and thus provide a channel clock fordetection of signal from the optical disc while the optical disc isrotated in the CAV mode.

[0012] For the optical disc described above, in the conventional art, aratio of spare area to data area is provided equally for every zone,about 5%, as shown in FIG. 5A. A zone has 875 more sectors than the nextmost-inwardly located zone because every zone has 875=(21000tracks/disc)/(24 zones/disc) tracks and the number of sectors per trackis increased by 1 for every track. Hence, more spare area is providedfor zones near the outer radii than for zones near the inner radii.

[0013] However, as shown in waveform 51 of FIG. 5A, experimentalobservations shows a tendency that more defects arise in zones near theinner or outer radii than in zones near the central radii because ofproblems of deposition by sputtering in the disc manufacturing process.The waveform 51 of FIG. 5(a) is parabolic.

[0014] Hence, in case where a constant ratio of spare area to data areais set to every zone, as shown in waveform 50 of FIG. 5A, it may happenthat, while zones near the inner or outer radii run short of the sparearea for replacement of defective areas on the data area, a large amountof spare area is not used in the zones near the central radii.

[0015] Moreover, in a conventional disc, there exists a ratio betweenthe size of the spare area and data area that is maintained constantthroughout the disc. Thus, conventional systems can recognize theboundary between the data area and the spare area without referring toany stored information concerning that boundary because the boundary hasalready been fixed by DVD disc physical specifications and can becalculated by a program in which the constant ratio is considered.

[0016] But, if the boundary is varied and boundary information is notwritten on a disc, the system can neither recognize exact boundary norcalculate boundary information by any program.

SUMMARY OF THE INVENTION

[0017] One object of the invention is to record boundary information ina predetermined location on a disc so that a system can recognize it andperform the proper operation of recording, reproduction and replacementof defective areas when the position of a boundary between the sparearea and the data area is varied, which object is not limited to a dischaving a plurality of zones or a constant ratio between the spare areaand data area.

[0018] It is an object of the present invention to provide a method andapparatus for manufacturing an optical recording medium in which theratio of a spare area to a data area varies according to the radialrange of the corresponding zones, respectively, and which hasinformation in a predetermined area of said medium needed todiscriminate between a data area and a spare area.

[0019] It is another object of the present invention to provide a methodand apparatus for writing/reproducing data to/from said opticalrecording medium in which the ratio of the spare area to the data areavaries according to the radial range of the corresponding zones,respectively, and has information in a predetermined area of said mediumneeded to discriminate between the data area and the spare area.

[0020] To achieve these and other objects, the present inventionprovides a method and apparatus for manufacturing an optical recordingmedium, the recording area being made up of a plurality of zones andhaving a data area and a spare area and information needed todiscriminate among the data area and the spare area. According to themethod and apparatus, in one or more zones, the ratio of the spare areato the data area varies depending on the corresponding locations orthose areas relative to the optical recording medium. Information neededto discriminate a data area and from a spare area, e.g., boundariesbetween the two areas which are changed with the ratios, is written as aphysical shape or as a normally written signal into a predetermined areaon the optical recording medium.

[0021] In the method and apparatus for writing data to said opticalrecording medium having information needed to discriminate among thedata area and the spare area according to the present invention, theratio of spare area to data area varies depending on the relativelocation of the zones on the optical recording medium. Informationneeded to discriminate a data area from a spare area, e.g., the boundarybetween the two areas, is recorded on a predetermined area on theoptical recording medium. Thereafter, when a write operation isrequested, the boundary information is used to locate the appropriatearea.

[0022] In the method and apparatus for reproducing data from an opticalrecording medium having information needed to discriminate the dataareas from the spare area according to the present invention,information needed to discriminate a data area from a spare area, theboundary between the two areas, is read out from a predetermined area onthe optical recording medium. Referring to the boundary information,data recorded in the data area is reproduced and data allocated todefective areas on the data area is moved into the corresponding regionof the spare area for replacement.

[0023] The foregoing and other objectives of the present invention willbecome more apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are included to provide afurther understanding of the invention, illustrate the preferredembodiment of this invention, and together with the description, serveto explain rather than limit the principles of the present invention.

[0025] In the drawings:

[0026]FIG. 1 is a layout figure representing a conventional partition ofrewritable area of a DVD-RAM;

[0027]FIG. 2 is a drawing explaining the conventional slippingreplacement algorithm in the write operation;

[0028]FIG. 3 is a drawing explaining a conventional linear replacementalgorithm in the reproduction operation;

[0029]FIG. 4 is a schematic view showing a conventional physicalconfiguration of recordable portions and header portions of a DVD-RAM;

[0030]FIG. 5A is a plot illustrating a conventional ratio of spare areato data area with respect to the radius;

[0031]FIG. 5B is a plot representing a distribution of ratios of sparearea to data area with respect to the radius;

[0032]FIG. 5C is a plot illustrating a different distribution of sparearea to data area ratios with respect to the radius, according to thepresent invention;

[0033]FIG. 6 is a schematic diagram of an apparatus for manufacturing anoptical recording medium having information needed to discriminate dataarea and spare area according to the present invention;

[0034]FIG. 7 is a schematic diagram of a beam permeating unit of theapparatus shown in FIG. 6;

[0035]FIG. 8(a)-8(c) illustrate control signals which are applied to thebeam permeating unit of FIG. 7;

[0036]FIG. 9 is a schematic diagram of another apparatus formanufacturing an optical recording medium having information needed todiscriminate data area and spare area according to the presentinvention;

[0037]FIG. 10 is a schematic diagram of an apparatus for writing data toan optical recording medium having information needed to discriminatedata area and spare area according to the present invention;

[0038]FIG. 11 is a schematic diagram of another apparatus for writingdata to an optical recording medium having information needed todiscriminate data area and spare area according to the presentinvention;

[0039]FIG. 12 is a schematic diagram of a partial configuration of a VDRplayer embodying an apparatus for playing an optical recording mediumhaving information needed to discriminate data area and spare areaaccording to the present invention;

[0040]FIG. 13 is a flowchart showing a method of manufacturing anoptical recording medium having information needed to discriminate dataarea and spare area;

[0041]FIG. 14 is a flowchart showing a method of writing data to anoptical recording medium having information needed to discriminate dataarea and spare area;

[0042]FIG. 15 is a flowchart showing a method of reproducing data froman optical recording medium having information needed to discriminatedata area and spare area;

[0043] FIGS. 16(a) and 16(b) illustrate the structure of a recordingmedium having a spare area and data area, and information needed todiscriminate among the data area and spare area according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The preferred embodiments of the present invention will bedescribed below in detail referring to the accompanying drawings.

[0045] Method and Apparatus for Manufacturing an Optical Disc

[0046]FIG. 6 shows an apparatus for manufacturing an optical disc havinginformation needed to discriminate data areas and spare areas accordingto the present invention. The apparatus comprises a ratio setting unit40 for keeping each zone's ratio of spare area to data area, whichdepends on its relative location on the optical disc; a laser beamgenerator 10 for generating a laser beam that is focused to aphotoresist on the optical disc; a laser beam permeating unit 100 forcontrolling selective transmission of the laser beam; a pickup locationdetector 30 for detecting a focused position of the transmitted laser onthe optical disc; and a laser beam transmission controller 50 forcontrolling the laser beam permeating unit 100.

[0047]FIG. 7 depicts the detailed configuration of the laser beampermeating unit 100, comprising a collimator 11 for collimating a laserbeam from the laser beam generator 10 to produce a parallel beam; asemitransparent plane 12 a and a reflecting plane 12 b for changing thetravel direction of the parallel beam; two acoustic optical modulators13 a and 13 b for selectively transmitting the reflected beams accordingto a land/groove identification signal and a pre-pit control signal; twoacoustic optical diffractors 15 a and 15 b for respectively fordiffracting beams reflected by reflecting planes 14 a and 14 b,depending on frequency of a high-frequency signal; a semitransparentplane 16 c and two reflecting planes 16 a and 16 b for producing a beamwhich is convergent on a photoresist on an optical disc from the twobeams from the acoustic optical diffractors; and a convergent lens 17.

[0048] The method for manufacturing an optical disc having informationneeded to discriminate data area and spare area will be explained indetail by referring to a flowchart of FIG. 13 and configurations ofFIGS. 6 and 7.

[0049] The user area of an optical disc is partitioned into 24 groups,so-called zones (S10). While reading data from every track in the samezone, the disc is in the CAV drive mode.

[0050] Each zone's ratio of spare area to data area is then determinedby taking into account its radial distance from the innermostcircumference and is kept in the ratio setting unit 40 (S11).Accordingly, the ratio of spare area to data area is different from onezone to another.

[0051] It should be noted that the ratios are determined on the basis ofthe frequency with which defects arise in the data area. Specifically,zones near the outer radii have more sectors than zones near the innerradii. Accordingly, one might expect that zones near the outer radiiwould need more spare area to provide replacement spaces for defectivesectors than zones near the inner radii. Such a variation in ratios ofspare area to data area would be determined such that the ratioincreases with increasing radius, as shown in waveform 52 of FIG. 5B.For context, the conventional art uniform 5% ratio is also depicted.

[0052] It has, however, turned out from experimental observations thatzones near the inner and outer radii are more vulnerable to defectoccurrence than zones near central radii because of some problems in thesputtering deposition process. Thus, inner and outer radii zones needrelatively more of the spare area than central radii zones. It is,therefore, preferred that the ratios of zones near the inner and outerradii be larger than those of zones near the middle or central radii, asshown in waveform 54 of FIG. 5C. Again, for context, the conventionalart uniform 5% ratio has been depicted.

[0053]FIG. 5(c) has 3 parts to the waveform 54, a linearly decreasingportion 56, an upwardly-opening center portion 58 and a linearlyincreasing portion 60. The portion 56 changes over to portion 58 at edge62, and the portion 58 changes over to the portion 60 at edge 64. Theslope of portion 56 is preferably the negative of the slope of portion60. The portion 58 is approximately parabolic. Alternatively, thewaveform 54 could be a parabolic.

[0054] Once each zone's ratio is stored and an optical disc begins to bemanufactured, the pickup location detector 30 starts to detect theposition of the convergence lens 17 on the optical disc (S12), anddetermines whether or not the current position is coincident with theboundary between data area and spare area in the current zone byreferring to the ratios stored in the ratio setting unit 40 (S13).

[0055] If the detected position is the boundary in the current zone, thelaser beam transmission controller 50 inputs a predetermined pre-pitcontrol signal to the laser beam permeating unit 100 so that informationindicating the boundary between data area and spare area is written to aheader portion in the form of pre-pit (S14). The heard portion is eitherthe last header portion in the data area or the first one in the sparearea in the current zone.

[0056] To be specific, a pre-pit control signal, which is ahigh-frequency ON/OFF signal shown in FIG. 8(b), is supplied to theacoustic optical modulator 13 b. Whether or not an incident laser beamis transmitted depends on change of its diffraction angle, which iscontrolled by the ON/OFF state of the pre-pit control signal. The beamthat is passed through the acoustic optical modulator 13 b is reflectedby the reflection plane 14 b and is then incident to the acousticoptical diffractor 15 b.

[0057] While header portions are formed, the wobble signal is notapplied to the acoustic optical diffractors 15 a and 15 b, thus thebeams incident to the acoustic optical diffractors 15 a are notdiffracted. And then, through a reflecting plane 16 b and a convergencelens 17, the beam that is passed through the acoustic optical modulator13 b and another beam that is passed through the acoustic modulator 13 acontrolled by a land/groove control signal are projected onto aphotoresist on a glass substrate, which rotates at a constant angularspeed. As a result, pre-pits are formed on header portions to indicatethe boundary between data area and spare area, as shown in FIG. 4. Thatis, for every zone, distinguishable pre-pits are made at a headerportion which is located at the desired boundary between data area andspare area. Thereafter, the stamper made by the above-described methodis used to manufacture optical discs having non-uniform ratios of sparearea and data area according to the present invention.

[0058] Unlike the foregoing embodiment, it is possible to writeinformation notifying the start and end portion of the data area to aheader portion that is located at the beginning of the data area, in theform of pre-pits. In this case, the pickup location detector 30 detectsthe start portion of each zone, and every time it is detected, thepre-pit control signal is controlled by the laser beam transmissioncontroller 50 so that a predetermined number of pre-pits is madephysically on the optical disc.

[0059] Instead of forming the distinguishable pre-pits at the boundarybetween data area and spare area, it is also possible that, at intervalsof a predetermined unit area, e.g., every time the pre-pit are formed,information indicating whether the area is used for a data area or aspare area is additionally written to the start header portion of theunit area in the form of pre-pits.

[0060]FIG. 9 shows a block diagram of another apparatus formanufacturing an optical recording medium having information needed todiscriminate the data area and spare area according to the presentinvention. This embodiment differs from the embodiment of FIG. 6 inthat, after an optical disc is made by using a stamper manufactured bythe conventional methods, information needed to discriminate the dataarea and spare area in each zone is written to the optical disc throughthe same operation as the data recording operation.

[0061] The apparatus according to this embodiment comprises a ratiosetting unit 40 for keeping each zone's ratio of spare area to dataarea; an optical pickup 101 for reading/writing data from/to an opticaldisc; a pickup location detector 30 for detecting the current positionof the optical pickup from data which is read out from the optical disc;and a data generator 60 for generating data needed to mark the boundarybetween data area and spare area and supplying it to the optical pickup101 by taking into account the position of the optical pickup 101.

[0062] In this embodiment, based on information on each zone's ratio ofspare area and data area and pre-pits on header portions, the opticalpickup location detector 30 checks whether or not the current positionof the optical pickup 101 is coincident with a desired boundary betweendata area and spare area in each zone, as in the foregoing embodiment ofFIG. 6. Each time the boundary is detected, the data generator 60 inputsdata needed to discriminate the two areas in each zone to the opticalpickup 101 so that the data is written to a header portion or data areaat the boundary point.

[0063] As another method, every time a boundary between data area andspare area is detected, location information on the boundary is added toa memory sequentially. Once detection of boundaries of all the zones iscompleted, the data generator 60 generates an information table whichcontains each zone's boundary from the stored location information andinputs it to the optical pickup 101, so that the information table iswritten in other areas than data area or spare area such as lead-in areaand lead-out area.

[0064] Method and Apparatus for Writing Data to the Optical Disc

[0065]FIG. 10 shows a block diagram of an apparatus for writinginformation on a partition of each zone into data area and spare areafor a recordable area of an optical disc which is made up of 24 zones,in which only a wobble signal and pre-pits are formed (not formattedyet), according to the present invention. This apparatus comprises aratio setting unit 140 for keeping each zone's ratio of spare area todata area, which depends on its relative location on the optical discDR; an optical pickup 1 for reading/writing data from/to the opticaldisc; a signal decoder 130 for decoding a signal received from theoptical disc 1 and thus obtaining the current position of the opticalpickup 1 from the decoded data; a data generator 150 for generating dataneeded to indicate the boundary between a data area and a spare area; awrite signal processing unit 170 for converting the boundary indicationdata into a pit signal; a write laser controller 180 for controlling aperiod of time in which a laser beam of the optical pickup 1 isactivated according to the pit signal; and a controller 190 forcontrolling the overall write operation.

[0066] The operation of the apparatus configured as above is describedbelow with reference to a flowchart of FIG. 14.

[0067] Under the state where non-uniform ratios of spare areas to dataareas are stored in the ratio setting unit 140, as shown in FIGS. 5B and5C, if an initialization operation such as a format command is issued(S31), the controller 190 starts to execute the operation to mark theboundary of the two areas in each zone on an optical disc. Thecontroller 190 rotates an optical disc DR and drives the optical disc 1(S32). When necessary, initialization data is sent to the write signalprocessing unit 170 so as to write the initialization data to theoptical disc.

[0068] Each zone's ratio of spare area to data area is then retrievedfrom the ratio setting unit 140 (S33). Next, while the signal decoder130 detects the current position of the optical pickup 1 (S34), itchecks whether or not the current position is coincident with thedesired boundary between the data area and the spare area in the currentzone (S35).

[0069] If they are matched, the data generator 150 generates andsupplies data needed to indicate the boundary between data area andspare area to the write signal processing unit 170. By the write lasercontroller 180, the data is then written at the boundary location on theoptical disc, or either the start location of the spare area or the endlocation of the data area (S36).

[0070] Unlike the foregoing embodiment, it is possible that, every timethe signal decoder 130 detects the start location of each zone duringmovement of the optical pickup, a pair of the start sector number andend sector number of each zone's data area is generated by the datagenerator 150 and is then written to a non-user data area preceding thedata area (S39).

[0071] Instead of the boundary between a data area and a spare area, itis also possible that, at intervals of a predetermined area, e.g., forevery set pre-pits formed on a header portion or in the unit of a sectoror an ECC block, information indicating whether each one of the unitarea is used for data area or spare area is additionally written to anon-user data area in the unit area which is provided at intervals ofthe chosen unit area.

[0072] Furthermore, information on all the boundaries between data areaand spare area, which is represented by the associated sector numbers,may be written at a predetermined area in either the lead-in area or thelead-out area.

[0073]FIG. 11 shows a block diagram of an apparatus for writing datainto an optical disc in which the ratio of spare area to data area isdifferent from one zone to another, and which contains informationneeded to discriminate data area and spare area in each zone. Theapparatus comprises an optical pickup 1 for reading/writing data from/tothe optical disc; a signal decoder 131 for obtaining data from aread-out signal received from the optical pickup 1; a pickup locationdetector 132 for detecting the current position of the optical pickup 1from the obtained data; a data generator 150 for generating data neededto discriminate data area and spare area; a write signal processing unit170 for converting the data to be recorded into a pit signal; a writelaser controller 180 for controlling a laser beam of the optical pickup1; and a controller 191 for controlling the write signal processing unit170.

[0074] In the apparatus configured as above, once a write operation isissued, the signal decoder 131 extracts positional data out of a signalread out from the optical disc by the optical pickup 1. Then, thepositional data is sent to the controller 191 which controls theoperation to obtain location of the data area in the current zone inwhich the optical pickup is located.

[0075] The start and end of the data area in the current zone which isdetected by the pickup location detector 132 are obtained by using thepositional data. Once the location of the data area is obtained, thecontroller 191 controls the write signal processing unit 170 so thatdata to be recorded (including data temporarily stored in a bufferduring the operation to locate data area) is processed and is thenwritten to the optical disc.

[0076] During the write operation, the controller 191 checks if theoptical pickup reaches the end of the data area in the current zone byusing the optical pickup's location obtained by the pickup locationdetector 130 or information on the area type obtained by the signaldecoder 131. If the end of the data area is detected, the data beingrecorded is no longer supplied to the write laser controller 180 and theoptical pickup is maintained in a ready state before it is moved to thenext zone.

[0077] Then, if the optical pickup starts to be moved to the next zone,the start and end location of the data area in the next zone areobtained in the same way as before, and thus the write operation isresumed at the data area in the next zone.

[0078] Method and Apparatus for Reproducing the Optical Disc

[0079]FIG. 12 shows a block diagram of an apparatus for reproducing datafrom an optical disc having information needed to discriminate data areaand spare area, which was made by the above-mentioned manufacturing andwriting apparatus. The apparatus comprises an optical pickup 1 forreading/writing data from/to the optical disc; a signal decoder 231 forobtaining data by decoding the signal read out from the optical pickup1; a pickup location detector 232 for detecting the current position ofthe optical pickup 1 from the obtained data; a defect checking unit 240for checking the presence of defects in the obtained data in the unit ofsector; a memory 220 for temporarily storing data during replacementoperation; a pickup driving unit 260 for driving the optical pickup 1 toa spare area assigned to the zone in which defective sector(s) aredetected; a write signal processing unit 270 for converting data to berecorded into a pit signal; a write laser controller 280 for controllinga period of time in which the laser beam of the optical pickup 1 isactivated; and a controller 300 for controlling the whole operation ofthe above-described components.

[0080] The operation of the apparatus of FIG. 12 is described below indetail by referring to a flowchart of FIG. 15.

[0081] Once the optical disc is loaded into the reproducing apparatus(S50), the optical pickup 1 is moved to a lead-in area or lead-out areain order to read out PDL and SDL, together with information on locationsof data area and spare area in each zone, and store them in the memory220 (S51).

[0082] After that, once a reproduction operation is issued (S52), datastarts to be read out from the optical disc. During a read-out process,by referring to the PDL and SDL in the memory 220, sectors listed in thetwo defect lists are skipped so as not to read out data from thosedefective sectors.

[0083] For non-defective sectors, data is obtained from the optical discby the signal decoder 231 (S53). By using physical identification (PID)contained in the obtained data, the defect checking unit 240 then checksif each sector is defective (S54). If it is determined that the sectoris a defective one, the location of data area and spare area in thecurrent zone to which the defective sector belongs is read from thememory 220 by the controller 300 (S55). And then, by using the locationinformation, the pickup driving unit 260 moves the optical pickup 1 tothe spare area assigned to the current zone (S56).

[0084] When the optical pickup 1 is located at an appropriate area ofthe spare-area, the data which has been recorded in an ECC blockcontaining the defective sector, and which is now temporarily stored inthe memory 220 is supplied to the write signal processing unit 270. Bythe write laser controller 280, the data is then written to the sparearea (S57). After that, the optical pickup 1 is returned to the next ECCblock in the data area, the reproduction operation is resumed (S58). Atthe same time, location of the area in which the data is written on thespare area is added to the PDL/SDL loaded in the memory 220. Thus, inthe subsequent reproduction, the ECC block identified as defective isskipped and thus the corresponding ECC block on the spare area is readout.

[0085] As another embodiment, a user recordable area of the optical discis partitioned into a plurality of unit areas of equal size, eachbelonging to either a data area or a spare area, for example, for everypre-pit indicating a header portion or in the unit of sector or ECCblock. When defective sectors are detected during reproduction, datathat has been recorded on defective sectors are moved to the unit areasassigned to the spare area, which are identified on the basis of theinformation indicating the type of unit area.

[0086] During the reproduction operation, i.e., while the signal decoder231 obtains data from a signal read out by the optical pickup 1 andstores them in the memory 220, the pickup location detector 232 detectsthe end location of the data area in the current zone from the dataobtained from the signal decoder 231.

[0087] Specifically, the pickup location detector 232 checks if theoptical pickup 1 is located at the end of the data area in the currentzone by comparing positional information contained in the data obtainedby the signal decoder 231, e.g., the sector identification number withpositional data of the data area and the spare area, or by identifyingpositional data indicating whether the unit area belongs to a data areaor a spare area. Once the end of the data area in the current zone isdetected, the pickup location detector 232 sends the end detectionsignal to the controller 300. And then, the operation of the signaldecoder 231 is stopped and the optical pickup 1 gets ready to move thenext zone, under control of the controller 300.

[0088] If the optical pickup 1 starts to be moved to the next zone, thestart location of the data area in the next zone is obtained in the sameway as before, and thus data recorded in the next zone is reproducedcorrectly.

[0089]FIG. 16(a) illustrates a recording medium structured and arrangedin accordance with a preferred embodiment of the present invention. Therecording medium of FIG. 16(a) has lead-in area 161, spare area 162,data area 163 and lead-out area 164. Data area 163 has a series of zonesindicated by broken lines. The recording medium of FIG. 16(a) isstructured such that lead-in area 161 is followed by spare area 162,which is followed by data area 163, which is followed by lead-out area164. Lead-in area 161 and lead-out area 164 are structured and arrangedto store information needed to discriminate among the spare area anddata area.

[0090]FIG. 16(b) also illustrates a recording medium structured andarranged in accordance with a preferred embodiment of the presentinvention. Like the recording medium of FIG. 16(a), the recording mediumof FIG. 16(b) has a lead-in area (not shown), a spare area 162, a dataarea 163, and a lead-out area (not shown). As demonstrated by FIG.16(b), the size of spare area 162 may be changed based on the number ofdefective sectors on the recording medium, particularly within data area163. Specifically, as the number of defective sectors increases, thesize of the spare area is reduced. FIG. 16(b) illustrates an example inwhich the recording medium has four (4) defective sectors, causing adecrease in the size of the spare area 162 by four (4) sectors. In thisexample, due to the existence of defective sectors, the original startposition of data area 163 is moved from a position corresponding toreference number 1631 to a position corresponding to reference number1632.

[0091]FIG. 16(b) includes reference arrows designated by referencenumerals 1634 and 1635. Reference arrow 1634 is used to illustrate aprocess in which the entire recording medium is scanned for defectivesectors. Reference arrow 1635 is used to designate the process ofassigning logical sector numbers (LSN) to sectors not deemed defective,beginning with the sector shown at reference number 1636. Through thisprocess, information regarding a boundary between the data area andspare area is written as the first and last sector number of the sparearea in DMA (Defective Management Area), allocated in the lead-in andlead-out areas.

[0092] The present invention makes it possible to avoid extra orinsufficient allocation of spare areas on the optical recording mediumby apportioning each zone's ratio of spare area to data area unequallybased on experimental observations on the frequency with which defectsarise with respect to each zone's relative location. Therefore, thepresent invention provides a way of reducing the possibility of thatsome zones run short of spare area or have excessive spare area,resulting in a more efficient use of the optical recording medium.

[0093] The foregoing is provided only for the purpose of illustrationand explanation of the preferred embodiments of the present invention,so changes, variations and modifications may be made without departingfrom the spirit and scope of the invention.

What is claimed is:
 1. A method for writing to an information recordingmedium having a data area for recording data and a spare area forreplacing defective units within said data area, wherein a boundary onsaid information recording medium between said data area and said sparearea is variable, the method comprising: writing information to apredetermined area on said information recording medium, saidinformation concerning the variable boundary between said data area andsaid spare area; and controlling an operation for recording of defectiveunits on said information recording medium based on said informationconcerning the variable boundary.
 2. A method according to claim 1,wherein said data area is divided into a plurality of data area partsthat are positioned adjacent to each other, and said spare area isdivided into a plurality of spare area parts that are positionedadjacent to each other.
 3. A method according to claim 1, wherein saidpredetermined area is at least one of a lead-in area and a lead-out areaon said information recording medium.
 4. A method according to claim 1,wherein said boundary information is sector address informationcorresponding to at least one of said data area and said spare area. 5.An apparatus for writing to an information recording medium having a,data area for recording data and a spare area for replacing defectiveunits within said data area, wherein a boundary on said informationrecording medium between said data area and said spare area is variable,the apparatus comprising: writing circuitry to write informationconcerning the variable boundary between said data area and said sparearea to a predetermined area on said information recording medium; and acontroller to control an operation for recording of defective units onsaid information recording medium based on said information concerningthe variable boundary.
 6. An apparatus according to claim 5, whereinsaid data area is divided into a plurality of data area parts that arepositioned adjacent to each other, and said spare area is divided into aplurality of spare area parts that are positioned adjacent to eachother.
 7. An apparatus according to claim 5, wherein said predeterminedarea is at least one of a lead-in area and a lead-out area on saidinformation recording medium.
 8. An apparatus according to claim 5,wherein said information concerning the boundary is sector addressinformation corresponding to at least one of said data area and saidspare area.
 9. A method for reading from an information recording mediumhaving a data area for recording data and a spare area for replacingdefective units within said data area, wherein a boundary on saidinformation recording medium between said data area and said spare areais variable, the method comprising: reading information from apredetermined area on said information recording medium, saidinformation concerning the variable boundary between said data area andsaid spare area; and controlling an operation for reading of defectiveunits on said information recording medium based on said informationconcerning the variable boundary.
 10. A method according to claim 9,wherein said predetermined area is at least one of a lead-in area and alead-out area on said information recording medium.
 11. A methodaccording to claim 9, wherein said boundary information is sectoraddress information corresponding to at least one of said data area andsaid spare area.
 12. An apparatus for reading from an informationrecording medium having a data area for recording data and a spare areafor replacing defective units within said data area, wherein a boundaryon said information recording medium between said data area and saidspare area is variable, the apparatus comprising: reading circuitry toread information from a predetermined area on said information recordingmedium, said information concerning the variable boundary between saiddata area and said spare area; and a controller to control an operationfor reading of defective units on said information recording mediumbased on said information concerning the variable boundary.
 13. Anapparatus according to claim 12, wherein said predetermined area is atleast one of a lead-in area and a lead-out area on said informationrecording medium.
 14. An apparatus according to claim 12, wherein saidinformation concerning the boundary is sector address informationcorresponding to at least one of said data area and said spare area.